1. Field of the Invention
This invention relates to highly active catalysts for highly stereospecific polymerization of .alpha.-olefins and to polymerization processes employing such catalysts. In particular, the present invention is suitable for polymerizing stereospecifically propylene, butene-1, 3-methylbutene-1, pentene-1, 4-methylpentene-1 and the like, also for copolymerizing the .alpha.-olefin with ethylene or other .alpha.-olefins, and further for polymerizing ethylene with better efficiency.
2. Description of the Prior Art
It has been well known that stereospecific polymers are produced by using a Ziegler-Natta catalyst system comprising a transition metal compound of a metal Groups IV to VIA of the Periodic Table and an organo-metallic compound of a metal of Groups I to III of the Periodic Table. Particularly a combination of a titanium halide and an organoaluminum compound such as triethylaluminum or diethylaluminum chloride is widely used in industrial production as a catalyst for stereospecific polymerization of .alpha.-olefins.
Polymerization of .alpha.-olefins such as propylene carried out with this type of catalysts results in a relatively high stereospecificity, which is shown by a ratio of boiling n-heptane insoluble polymers to soluble polymers, i.e., stereospecific polymers. However, the polymerization activity of the catalyst is not fully satisfactory and removal of catalyst residue from the polymer formed is necessary.
As highly active catalysts for olefin polymerization, many catalysts have been proposed which comprise an inorganic magnesium compound or organomagnesium compound and a titanium or vanadium compound or these two components plus an electron donor.
As the inorganic magnesium catalyst, for example, Polymer Letters, Vol. 3, p 855-857 (1965) describes the polymerization of propylene using a catalyst obtained by reacting magnesium chloride with titanium tetrachloride and, if necessary, adding triethylaluminum as an additive thereto. In this case, addition of an electron donor such as ethyl acetate improves the stereospecificity of the polymer formed. Further Japanese Patent Publication No. 12105/1964 describes an increase in the amount of hydrocarbon insoluble polymers in the polymers obtained when an additive such as ethyl acetate is added to the polymerization system where a combination of titanium tetrachloride-covered particles of magnesium chloride or cobalt chloride with a metal alkyl such as triethylaluminum and diethylaluminum chloride is employed as the catalyst. This Japanese Publication also describes the preparation of a novel catalyst obtained by pulverizing a metal salt such as magnesium chloride, adding a titanium tetrachloride solution to the metal salt as the support and shaking the mixture.
As another category of organomagnesium catalysts, Japanese Patent Publication No. 31968/1971 describes the polymerization of alkenes at a temperature of at least 110.degree. C. using a catalyst obtained by adding an alkanol, an alkenol, an alkanolate, an alkenolate, a carboxylic acid, an ester or salt of a carboxylic acid, an aldehyde or a ketone before, at or after mixing an aluminum halide with a titanium compound. According to this method the stay period of time for a polymer solution in the polymerization zone is advantageously controlled within 10 minutes, preferably 5 minutes but the amount of boiling n-heptane insoluble polymers in the polymers formed is not sufficiently high. Moreover, the polymer yield per solid catalyst component is not sufficient and the polymers produced contain a high amount of a halogen atom which causes corrosion of the apparatus for producing polyolefins and the molding machines, and accordingly the properties of the products are not fully satisfactory.
According to Japanese Patent Application (OPI) Nos. 40696/1978, 70991/1978, 100986/1978, 5893/1979, 127889/1979 and 136591/1979, there have been proposed excellent catalysts for polymerizing olefins which comprise (a) a solid component obtained by contacting a hydrocarbon soluble organomagnesium component with a chlorosilane compound having a H-Si bond, a titanium compound and an electron donor and (b) an organometallic compound. Also according to Japanese Patent Application (OPI) Nos. 26905/1981, 28206/1981, 32504/1981, 47408/1981 and 5905/1981, there has been proposed the polymerization of ethylene using such catalysts, and it would be highly desirable to provide catalysts which give polymers having greater particle diameters and to further simplify the preparation method of the catalysts.
As a result of the study on the catalyst system for stereospecific polymerization of .alpha.-olefins it has now been discovered that by using, as the catalyst, a reaction mixture obtained by reacting a specific titanium compound and a specific electron donor with a reaction product having been obtained by reacting a specific organomagnesium compound with a chlorosilane compound having a Si-H bond, in combination with an organometallic compound, there can be obtained excellent catalyst suitable for polymerization of .alpha.-olefins.